1. Field
The present disclosure relates to liquid crystal (LC) compositions, i.e., liquid-crystalline media, for high-frequency technology, especially for high-frequency devices, in particular antennas, tunable filters, switching devices operated in the microwave region. These components function based on changing dielectric properties of liquid-crystalline media under an applied voltage.
In addition, the present disclosure relates to novel mesogenic compounds.
2. Description of the Related Art
Liquid-crystalline materials have been used for a long time in liquid crystal displays in order to display information.
Liquid-crystalline materials for high-frequency technology have been disclosed in various patent documents, especially in US 2014/0021409 A1, DE 10 2004 029 429, US 2013/0292608 A1, US 2012/0182200 A1, US 2012/0205583 A1, US 2012/0292608 A1, US 2012/0273724 A1, US 2013/0221274 A1, and US 2014/0008575 A1.
In these patent documents, various liquid crystalline bistolan compounds, also known as triphenyldiacetylenes, are disclosed. For example, US 2012/0182200 A1 discloses various liquid crystalline bistolan compounds containing unfluorinated alkyl, unfluorinated alkoxy or unfluorinated alkenyloxy as a lateral substituent, of the formula:

However, these compounds are afflicted with a serious disadvantage. The stability of the media is low, in particular under UV irradiation and at high temperatures.
US 2014/0021409 A1 discloses various liquid crystalline bistolan compounds containing different types of a lateral substituent and different polar groups, such as CN, NCS, SF5, CF3, OCF3, F, or Cl, of the formula:

However, these compounds are afflicted with a serious disadvantage. The stability of the media is low, in particular under UV irradiation and at high temperatures.
For liquid-crystalline bistolan compounds containing a lateral methyl group, Hsu, C. S., Shyu, K. F., Chuang, Y. Y. and Wu, S.-T., Liq. Cryst., 27(2), (2000), pages 283-287 proposes to use thereof in liquid crystal optically phased arrays. However, these compounds are afflicted with a serious disadvantage. The stability of the media is low, in particular under UV irradiation and at high temperatures.
Herman, J., Dziaduszek, J., Dabrowski, R., Kedzierski, J., Kowiorski, K., Sai Dasari, V., Dhara, S., Kula, P., Liq. Cryst., 40(09), (2013), pages 1174-1182, mentions new laterally alkyl-substituted quaterphenyl and phenylethynyltolane liquid crystals with isothiocyanate terminal group, which are proposed for use as high birefringence materials for different applications, in particular for high-frequency devices. However, these compounds are afflicted with serious disadvantages. Most of them result, besides other deficiencies, in disadvantageously high losses and/or inadequate phase shifts or inadequate material quality.
U.S. Pat. No. 7,183,447 discloses various laterally fluorinated, mesogenic quaterphenyl compounds. However, these compounds are afflicted with serious disadvantages. Most of them result, besides other deficiencies, in disadvantageously high losses and/or inadequate phase shifts or inadequate material quality.
U.S. Pat. No. 7,211,302 discloses, inter alia, liquid-crystalline media which comprise, besides polar terphenyl compounds, various laterally fluorinated, mesogenic quaterphenyl compounds and also comprise a small amount of quaterphenyl compounds of the formula:

in order to improve the stability of the media, in particular under UV irradiation. However, these compounds are afflicted with serious disadvantages. Most of them result, besides other deficiencies, in disadvantageously high losses and/or inadequate phase shifts or inadequate material quality.
Recently, however, liquid-crystalline media have also been proposed for use in components for microwave technology, such as, for example in DE 10 2004 029 429 A.
Liquid crystalline media which comprise, for example, compounds of the formula:
are proposed for use in components for high-frequency technology, for example, in A. Lapanik, “Single compounds and mixtures for microwave applications, Dielectric, microwave studies on selected systems”, dissertation, Technical University of Darmstadt, 2009, (D17).
However, these compositions are afflicted with serious disadvantages. Most of them result, besides other deficiencies, in disadvantageously high losses and/or inadequate phase shifts or inadequate material quality. The stability of the media is low, in particular under UV irradiation.
Novel liquid-crystalline media having improved properties are thus necessary. In particular, the loss in the microwave region and/or millimeter wave region must be reduced and the material quality factor be improved.
Thus, there is a considerable demand for liquid-crystalline media having suitable properties for corresponding practical applications.